It is known that attempts have been made to produce a lubricant universally compatible with two-stroke and/or four-stroke internal combustion engines. The lubricants generally contain a number of different performance additives that are not necessarily designed for application in e.g., a four-stroke motorcycle engine where crankcase oil viscosity is required whilst also requiring properties compatible with extreme pressures and temperatures associated with a gearbox, transmission or clutch. Consequently, many additives have properties that adversely affect engine performance or fuel economy.
Kasai et al. (2003 JSAE/SAE International Spring Fuels & Lubricants Meeting, Yokohama, Japan, May 19-22, 2003, Paper title Effect of Engine Oil Additives on Motorcycle Clutch System (SAE2003-01-1956 or JSAE 20030105) discloses borated dispersant in combination with detergents or zinc dithiophosphate as being suitable for friction control. Kasai et al. further states that engine oils containing friction modifiers cannot be applied in a 4-stroke motorcycle engine because they decrease clutch capacity.
U.S. Pat. No. 6,525,004 discloses a composition containing a borated hydrocarbyl succinimide dispersant and a phosphorus compound for use in 2-cycle and small engine four-cycle engines.
It would be advantageous to have a method of lubricating an internal combustion engine with at least one of a crankcase, a gear, a transmission system and a wet-clutch while imparting friction control. The present invention provides a method of lubricating an internal combustion engine while imparting friction control.